In fire-prone forests, tradeoffs exist between maximizing and stabilizing forest carbon stocks. In Southwestern ponderosa pine forests management activities to reduce the risk of stand-replacing fire initially decrease total ecosystem carbon, but prior research demonstrates treated forests can store more carbon over time than unmanaged forest, because fire severity is reduced. Climate projections for the southwestern US indicate a drier future is likely, due to increasing temperature. These changes have the potential to impact forest carbon sequestration and post-fire recovery. Given the potential impacts of changing climate, I sought to quantify the effects of forest treatments to reduce stand-replacing fire risk under current and projected climate. I used the LANDIS-II forest landscape model to simulate carbon dynamics under early (2010-2019), mid (2050-2059), and late (2090-2099) century climate projections for an 11,000 ha landscape in northern Arizona. I developed monthly distributions of temperature and precipitation using 1/8 degree bias-corrected and downscaled CMIP5 climate model projections forced with RCP 8.5. I ran 100 year simulations of two different treatments (no management, thin and prescribed burning) with wildfire using climate projections from each of the three time periods.
In the absence of treatment, total ecosystem carbon in year 100 ranged from 8408 g C m-2 for late-century climate to 9218 g C m-2 for early-century climate and cumulative net ecosystem exchange ranged from 1242 g C m-2 for late-century climate to 1911 g C m-2 for mid-century climate. Thinning and burning treatments had higher end-of-simulation total ecosystem carbon for all climate projections (11,554-11,708 g C m-2). This result was driven by the effects of treatment moderating wildfire severity. Under all climate scenarios, treatments increased cumulative net ecosystem exchange because wildfires killed fewer trees. While the increase in cumulative net ecosystem exchange for the thin and burn under early and mid-century climate increased nearly three-fold relative to no management, late-century cumulative net ecosystem exchange for the thin and burn scenario was four times higher than in the absence of treatment. These results suggest that in addition to altering wildfire behavior and its effects on the ecosystem, treatments may help maintain productivity in a drier future by reducing water competition.